The present invention is related to a manually operated switch device for the control of electrical equipment.
For switches employed in electrical equipment, the switch position or the switch status must be secured so that an uncontrolled change of the switch status cannot occur. An inadvertent starting of an electrical apparatus may occur due to, e.g., vibration or a strong shock which causes the movement of the switch into a wrong position resulting in dangerous, hazardous situations, such as the unintentional starting of equipment. Inadvertent switching-on of electric power in a circuit may also be hazardous during, e.g., maintenance operations. Correspondingly, unintentional toggling of a switch into the zero position, that is, switching off the current from an electric circuit may cause machinery damage due to uncontrolled stopping of actuators. Due to such problems, reliable latching of equipment switches in their ON and OFF positions, must be secure with the help of, e.g., spring-loaded means.
Positive latching of a switch position can be implemented by means of, e.g., a cam attached to the switch operating shaft, whereby the cam is followed by a spring-loaded lever. The lever is provided with a guide slot suited to accommodate a guide pin fixed to the body structure of the switch. The loading spring of the lever is adapted about the lever and compressed between the guide pin and the meeting point of the lever with the cam. When the switch is in its ON position or its OFF position, respectively, the spring latches the switch positively in its set position and prevents uncontrolled rotational motion of the switch operating shaft. As the switch operating shaft is rotated, the spring is compressed between the guide pin and the cam tip. After the cam tip is rotated into its top dead center position, the toggling point of the detent cam/lever system is attained and as the cam is further rotated over its TDC position, the spring pushes the cam and the attached operating shaft of the switch into its opposite position.
However, such a switch construction has some drawbacks. Although the spring can latch the switch positively in a correct position at the ends of the shaft rotational travel, the operation of the switch is rather uncontrolled in the middle of the shaft rotational travel. In the TDC position of the detent cam/lever mechanism, the spring force is oriented parallel to the longitudinal axis of the detent cam/lever combination, thus being exerted onto the switch operating shaft and not exerting a rotational force on the switch operating shaft and the guide pin. Consequently, this sector of the rotational travel forms an undetermined position of the switch setting, in which the switch may remain after operation by a careless user. The mutual friction between the switch members makes such a position uncontrollable and relatively easily permits the switch to assume this intermediate position. As the intermediate position coincides with the TDC position of the detent cam/lever mechanism, the position is quite labile. Therefore, a switch left in this intermediate position may readily toggle from this intermediate position due to, e.g., a small shock into either limit position. As a result, such an uncontrolled change of switch position can cause an inadvertent starting of equipment or switching-on of power in an electric circuit supposed to be at zero voltage. Obviously, a hazardous situation occurs.
In addition to the discussion above, a conventional switch has the drawback that the operating speed of the switch is dependent on the operator action. This property degrades the electrical performance specifications of the switch. When the switch is operated using, e.g., too low a torque, the switching action does not take place at a sufficient speed, whereby an arc will be formed between the contacts that can destroy the switch very quickly as the energy released by the arc obviously has the greater burning effect the longer the arc is maintained. In addition to inadvertent arcing, the switch can be willfully misused by keeping the switch in a position that makes a marginal connection via the burning arc. Obviously, such a misuse destroys the switch very rapidly.
Disclosed in FI Pat. No. 93,502 is a switch device in which the switch body is provided with at least one linearly movable slide member with contacts adapted to cooperate with the stationary contacts of the switch. To the slide member, via at least one spring-type member, is connected, parallel with the slide member, a movable spring-arming plate which during the motion of said plate causes the slide member to correspondingly move under the force exerted by said springs. While this switch device embodiment provides a reliable and rapid switching action and unambiguous position indication, the structure of the contact surfaces permits operation of this device alone at relatively low currents.